The IEEE standard, "P1394 Standard For A High Performance Serial Bus," Draft 8.0v2, Jul. 7, 1995, is an international standard for implementing an inexpensive high-speed serial bus architecture which supports both asynchronous and isochronous format data transfers. Isochronous data transfers are real-time transfers which take place such that the time intervals between significant instances have the same duration at both the transmitting and receiving applications. Each packet of data transferred isochronously is transferred in its own time period. The IEEE 1394 standard bus architecture provides multiple channels for isochronous data transfer between applications. A six bit channel number is broadcast with the data to ensure reception by the appropriate application. This allows multiple applications to simultaneously transmit isochronous data across the bus structure. Asynchronous transfers are traditional data transfer operations which take place as soon as possible and transfer an amount of data from a source to a destination.
The IEEE 1394 standard provides a high-speed serial bus for interconnecting digital devices thereby providing a universal I/O connection. The IEEE 1394 standard defines a digital interface for the applications thereby eliminating the need for an application to convert digital data to analog data before it is transmitted across the bus. Correspondingly, a receiving application will receive digital data from the bus, not analog data, and will therefore not be required to convert analog data to digital data. The cable required by the IEEE 1394 standard is very thin in size compared to other bulkier cables used to connect such devices. Devices can be added and removed from an IEEE 1394 bus while the bus is active. If a device is so added or removed the bus will then automatically reconfigure itself for transmitting data between the then existing nodes. A node is considered a logical entity with a unique address on the bus structure.
Each node on the IEEE 1394 bus structure has a 16 bit node ID. The node ID is the address that is used for data transmission on the data link layer. This allows address space for potentially up to 64K nodes on the bus structure. The node ID is divided into two smaller fields: the higher order 10 bits specify a bus ID and the lower order 6 bits specify a physical ID. The bus ID is assigned by a root node and the physical ID is assigned during a self identify sequence upon reset of the bus. Each physical ID field is unique in a single IEEE 1394 bus, but the physical ID field is not a fixed value for each node itself. The physical ID field is fixed for the position of the node. If a device is moved from one position in the IEEE 1394 bus to another position within the same IEEE 1394 bus, the device will have a different node ID because its physical ID will have a different value when in the new position.
Within each of the bus ID and physical ID fields a value of all logical "1"s is reserved for special purposes. Accordingly, this addressing scheme provides for up to 1023 busses, each with 63 independently addressable nodes. Each IEEE 1394 compatible device includes a node unique ID which is a 64 bit number saved within a configuration read-only memory (ROM) of the device. The node unique ID is permanent for each device and does not depend on the position of the device within an IEEE 1394 bus. The node unique ID is not used for addressing of data transmissions on the data link layer.
IEEE 1394 serial bus and other complex networks, although necessary in many environments, are very complex and difficult to maintain. It is desirable in such networks to have the ability to automatically configure and maintain a mapping of the devices within the network and their corresponding physical positions. For example, within an in-flight entertainment system implemented on an aircraft, it is likely that the airline responsible for the aircraft will periodically reconfigure the layout of the cabin or remove and replace seats and equipment within the cabin. In such instances, it is desirable for the in-flight entertainment system to have the ability to automatically map the devices to their corresponding physical position within the aircraft. Without this automatic configuration ability, this map or database of the devices to their physical position would have to be manually maintained and updated after installation of the system and when devices within the system are replaced or reconfigured. This type of manual method is labor intensive and will be subject to human error. Having the ability for the network to automatically map the devices to their physical position will reduce the possibility of this human error, allow flexibility for platform configuration changes and minimize the downtime of the network.
Including a database within the network which automatically maps devices to their corresponding physical location will also make it easy to complete device specific or user specific billing, easy to block service or types of services to particular devices and easy to personalize service to specific devices and users. Automatically maintaining such a configuration database also makes it easy to display the network configuration and topology of the devices for the use of both attendant and maintenance personnel.